To quote BA from the A-Team,

"I love it when a plan comes together." Congratulations on the results of all your hard work. Although the Saltire undergarments sound cute, I would go with something dark and nondescript to avoid the temptation to "show them off" which might then spoil the whole kilted event-----spandex training shorts work well and come in dark colors generally. No reason to take chances now.

Good luck, waiting for the grand photos.